An integrated methodology to evaluate permeability from measured microstructures

Most existing data on solids dewatering behavior are based on macroscale phenomena and are often empirically based, whereas challenges still remain for fundamental understanding at a much smaller length scale. Prediction of microscale properties is now possible with enabling technologies such as X-ray microtomography (XMT) for 3-D imaging of solid structures and the Lattice-Boltzmann method (LBM) for calculating their permeability. Microstructural information with a spatial resolution of up to a few microns per pixel can be obtained through XMT and can be used directly by the LBM-a digital equivalent of the conventional CFD that is more adept at dealing with solid boundaries of complex geometry such as filter media-to calculate flow distribution through the porous structure. An example of this approach using glass beads is described here, from which the permeability of sediments containing this material can be predicted on the basis of a bench-top test and the use of fluid flow simulations. The ability to derive performance information-such as fluid permeability from laboratory-based measurements of microstructure coupled with appropriate microscale physical simulations-has considerable potentials. It is proposed that the method may be used to predict trends such as the filtration behavior of porous structures under different states of compression. This offers a significant benefit in assisting the formulation design of flocculated materials pertinent to a number of industrial sectors wishing to design optimal filtration or relevant operations. (c) 2006 American Institute of Chemical Engineers.